In internal combustion engines of motor vehicles, a pressure measurement for ascertaining the combustion-chamber pressure is necessary, in order to obtain, in each instance, information regarding the pressures prevailing in the combustion chamber of the combustion engine. Information regarding the pressures prevailing in the combustion chambers in each instance may be used for determining the actual engine torque and monitoring the combustion (e.g. misfiring, knock) at in modern engine management systems.
An integrated silicon combustion-chamber pressure sensor is described on page 111 of the kraftfahrttechnischen Taschenbuch Automotive Engineering Paperback Book, 23rd edition, Braunschweig; Wiesbaden, Viehweg 1999, ISBN 3-528-03876-4. The silicon combustion-chamber pressure sensor includes a transmission impacting rod, a silicon platform that is used for applying force, as well as an integrated silicon pressure sensor. Situated on one side of the steel mounting plate is one or more connector pins, from which a connecting line runs to the integrated silicon pressure sensor. In this set-up, the silicon chip is not directly exposed to the high temperatures in a combustion chamber of an internal combustion engine. This is achieved, using a metallic separating diaphragm, as well as a sufficiently long impacting ride for force transmission. The silicon chip becomes a force sensor by micromechanically applying a platform in the center of the diaphragm. The compressive forces absorbed by the front diaphragm are introduced by the impacting rod with only a small amount of additional misrepresentation, via the platform, into the silicon sensor chip. This sensor chip is in a retracted (recessed) mounting position and is therefore only subjected to operating temperatures less than 150° C.
International Application No. WO 97/31251 A describes a combustion-chamber pressure sensor for ascertaining signs of knocking and misfiring. A fiber-optic combustion-chamber pressure sensor is integrated into a spark plug. The former is configured such that a conductor passes through the spark-plug body. A key-shaped (push-button-shaped) diaphragm having a non-uniform thickness reduces the mechanical load acting on the diaphragm and increases the reliability of the sensor. Excessive pressure acting on the combustion-chamber pressure sensor is reduced by forming angled sections on the diaphragm.
Micromechanical combustion-chamber pressure sensors have been shown in practice to be completely capable of being mass-produced, but they have considerable disadvantages. The micromechanical combustion-chamber pressure sensors have only a limited thermal resistance. However, since the micromechanical combustion-chamber pressure sensors must be installed as close to the combustion chamber as possible, they are subjected to higher temperatures, which places corresponding demands regarding the thermal resistance of such combustion-chamber pressure sensors. In addition, the conventional micromechanical combustion-chamber pressure sensors have the disadvantage, that their capability of being miniaturized is limited. Therefore, the micromechanical combustion-chamber pressure sensors used at present require larger mounting surfaces in the region of a cylinder head of a combustion engine. However, the cylinder head of a combustion engine represents a region of the combustion engine, at which the space is already limited due to the multitude of inserted or directly attached components.
Pressure sensors, which function according to the piezoelectric principle and require very expensive evaluation electronics, are also used to precisely determine inner cylinder pressures or combustion-chamber pressures of combustion engines. On the one hand, these pressure sensors are very precise, but, on the other hand, they are very expensive, and because of the voluminous evaluation electronics, they are only suitable for use on test stands and, in the best case, in experimental vehicles. In addition to this application, efforts are also underway to use the measurement of combustion chamber pressure in production engines, in order to achieve engine control based on combustion chamber pressure. However, combustion-chamber pressure sensors, which satisfy the high requirements for a production solution regarding price, handling, and service life while simultaneously satisfying the requirements for the accuracy of the combustion-chamber pressure measurement, are not obtainable on the market.